1. Field of the Invention
The present invention is directed to a therapy apparatus for locating and treating a zone in the body of a living subject with acoustic waves, of the type having a source of acoustic waves which generates therapeutic acoustic waves having a first frequency that are focused onto a zone of action and an acoustic locating means which transmits diagnostic acoustic waves having a second frequency, and which receives parts of the diagnostic acoustic waves reflected in the body of subject and, converts them into electrical signals which are used as image information with respect to the zone to be treated.
2. Description Of the Prior Art
Therapy systems which emit focused ultrasound waves as therapeutic acoustic waves and diagnostic ultrasound as diagnostic acoustic waves are employed, for example, for the treatment of pathological tissue (see, for example, European Application 0 339 639, corresponding to U.S. Pat. Nos. 5,150,712 and 5,143,073, and Ultrasound Intracavity System for Imaging, Therapy Planning and Treatment of Focal Disease", Sanghvi et al., Reprint from 1992, IEEE Ultrasonic, Ferroelectrics and Frequency Control Symposium). The pathological tissue is heated by the focused ultrasound waves. If the resulting temperatures lie below 45.degree. C., the cell metabolism is disturbed, resulting in a retardation of the growth, or a shrinking of, treated tissue mass, such as a tumor. This type of treatment is known as local hyperthermia. When temperatures beyond 45.degree. C. are achieved, the cell protein coagulates, with the result that the tissue is necrotized. This latter type of treatment is referred to as thermotherapy.
Different frequencies for the therapeutic and for the diagnostic ultrasound waves are employed in order to enable an optimum matching to the respective task, therapy or diagnostics. As a rule, the frequency of the therapeutic ultrasound waves will be selected relatively low for achieving low attenuation, whereas that of the diagnostic ultrasound waves will be selected relatively high in order to achieve a good topical resolution.
In known therapy systems of the type initially cited, the therapeutic ultrasound source and the ultrasound locating means can generally not be simultaneously operated, since the operation of the therapeutic ultrasound source leads to image disturbances in the image produced by the ultrasound locating means, so that a proper locating of the zone to be treated is not possible. Except in unusual cases wherein echo signals of the therapeutic acoustic waves are to be evaluated, for example as described in German OS 42 05 030, one usually proceeds as described in European Application 0 339 693 such that the therapeutic ultrasound source and the ultrasound locating means are operated in alternation, namely such that relatively long treatment intervals and relatively short locating intervals follow one another in alternation. This means that a continuous locating of the zone to be treated is not possible.
U.S. Pat. No. 4,584,880 discloses an ultrasound imaging apparatus wherein a filter having a bandpass-like filter characteristic is provided at the reception side. This filter is provided in order to be able to image regions lying deeply within the subject to be imaged with improved image quality. Since, in comparison to the emitted ultrasound pulses, the frequency spectrum of the received echo signals becomes lower in frequency as the depth from which the echo signals derive increases, the passband of the filter is shifted toward lower frequencies following each transmission of an ultrasound pulse (and the gain is increased at the same time). A continuous locating and monitoring of the zone to be treated would not be enabled, however, by applying these known measures in a therapy apparatus of the type initially cited.